Key pieces of DNA called telomeres, which indicate the ability of cells to replicate, are also linked to how young a person looks.

A telomere of shorter length is thought to signify faster ageing and has been linked to a number of diseases, such as cancer. The latest study, carried out in Denmark, was based on more than 387 twin pairs.

The results of the study, published online in the British Medical Journal (BMJ), showed that a person's perceived age — how old people think they look — was linked to how long they lived.

Over a seven-year follow-up, experts found that the bigger the difference in perceived age within a pair, the more likely that the older-looking twin died first.